Calculation of Biodiversity Net Gain

The High Court has refused a claim for judicial review of a challenge to a decision to redevelop Bristol Zoo Gardens to include 196 residential units (Class C3), the provision of community floorspace (Class E, F1 and F2) and open space with associated landscaping etc in Save Bristol Gardens Alliance Limited v Bristol City Council [AC-2024-CDF-000142]. The case relates to the ongoing redevelopment of Bristol Zoo following its relocation from Clifton.

The grounds of challenge were fundamentally related to whether or not the Defendant, Bristol City Council (“BCC”) had assessed correctly (1) the biodiversity net gain (“BNG”) calculations; (2) the sustainability credentials of the development, including the planning policy requirements for renewable energy and carbon; and (3) the implications for open space.

BNG: How should the “net gain” be calculated?

The case considered the policy background for requiring BNG. Since the initial preparatory work on the case had been commenced, and up to determination, Natural England (“NE”) had provided several revised metrics (Metric 3.0 had been updated by 3.1, and 4.0). Bristol Tree Forum contended that the most up-to-date version of the metric must be used in determining the application. Using updated versions of the metric, the Claimant argued that there would have been a net loss rather than a net gain of biodiversity.

Mould J provided a detailed analysis of the differences between the metrics and noted the fact that NE had provided clear guidance on the appropriateness of continuing to use a metric where work had been commenced under a previous iteration of the metric. In allowing the Interested Party to continue using Metric 3.0, the Court found there to be no error of law in the approach taken by BCC. The Planning Officer had not materially misled the committee [56] – [61]. The Court also noted that the practicalities of preparing projects for submission often entail considerable lead times. This will sometimes lead to work being undertaken using previous metrics.

Climate Change: How should a 20% reduction in CO2 be calculated?

The second ground of challenge related to the scheme’s ability to mitigate the impacts of climate change, having regard to the Bristol Core Strategy policy, which provides that developments are expected to deliver sufficient energy generation to reduce CO2 by “at least 20%”. The policy was silent on how the 20% should be calculated.

The heart of the dispute was whether the Building Regulations Part L 2013 (“L2013”) ought to have been used, or whether the interested party was required to use updated carbon factors present in the Building Regulations Part L 2021 (which only took effect in 2022) (“L2021”).

BCC, consistent with their own guidance, had continued to use the L2013 methodology [95]. This was summarised in the Planning Officer’s report, notwithstanding objections from the Claimant’s expert. The interested party had prepared the planning application for submission in accordance with BCC guidance, the relevant policies and practice note, and had used L2013, which was current at the time the application was prepared. This had estimated a reduction in CO2 of greater than 20%, in compliance with the policy.

The L2021 had only come into force two days after the application was validated [115], and therefore, it was acceptable to continue using L2013. This was ultimately a matter of discretion – a matter of planning judgment – and there was no requirement to rely upon the L2021 carbon factors. There were significant differences between L2013 and L2021 that the Planning Officer recognised, but they were not of such significance to make it unreasonable for the application to be assessed and determined using L2013 factors, in accordance with the guidance [119].

Public Open Space

BCC has a policy to protect Important Open Spaces. The Planning Officer scrutinised the proposal and noted the qualitative upgrade through enhancements to the physical features, the historic landscape, and the opening up of the site to the public, including public art and culture, play areas, and a lakeside garden.

The qualitative enhancements would mean an overall improvement in quantity and quality (per NPPF, then §99(b), now §104). This affirms the overall principle in R(Brommell) v Reading Borough Council [2018] EWHC 3529 (Admin). It was not a prerequisite to the proper application of §99(b) NPPF for the Planning Officer to make precise findings as to the amount of existing open space lost to the development and the amount of open space provided by way of replacement [146]. His planning judgment was that there would be a marked improvement over the existing position. There was no unlawfulness as a consequence [147].

This judgment provides a pragmatic approach to both BNG and carbon policies in the absence of mandated formulae for calculating the gains. It also reaffirms previous High Court authority on the flexibility in the overall judgment undertaken in relation to open space provision.

Peter Goatley KC and Sioned Davies are barristers at No5 Barristers Chambers. They acted for the successful Interested Party, Bristol, Clifton and West of England Zoological Society, instructed by Anne Harrison at DAC Beachcroft LLP.